Optical element

ABSTRACT

The invention has an object to provide an optical device which can directly and efficiently introduce a planar incident light as it is and can efficiently obtain a planar total reflected light on a desirable interface without using a light guiding plate or an optical waveguide, and is constituted by a reflector having no absorption without depending on an incidence angle.  
     The invention provides a planar optical device characterized by such a feature that when an incident light is introduced like a plane into the optical device, at least apart of the incident light thus introduced is totally reflected by an interface of layers constituting the optical device, while the incident light is not substantially emitted from an opposite side to an incident light introduction side.

FIELD OF THE INVENTION

[0001] The present invention relates to a planar optical device fortotally reflecting a planar incident light in a medium provided in thefront part of an optical path for the incident light, and moreparticularly to a technique for efficiently introducing the light to bereflected totally in the medium.

BACKGROUNDS OF THE ART

[0002] For example, in a liquid crystal display, a light guiding platefor guiding the light of a back light over a whole display screen isprovided on the back side of the display surface of a liquid crystalpanel. In the light guiding plate of this kind, an incident light isintroduced from the end face side of the light guiding plate or anoptical waveguide and is totally reflected and propagated in the lightguiding plate or the optical waveguide so that a planar total reflectedlight can be obtained efficiently.

[0003] Moreover, a reflector capable of carrying out an efficientreflection includes a film having a metal or a metallic surface. Inaddition, the reflector includes a multilayer film interference mirrorsuch as a dielectric multilayer film mirror.

[0004]FIG. 31 shows a state in which an incident light is introducedfrom a general light guiding plate and waveguide according to theconventional art. FIG. 31(a) shows a state in which the incident lightis introduced from the end face of the light guiding plate and istotally reflected and guided in the light guiding plate, and FIG. 31(b)shows a state in which a prism is provided on the end of the lightguiding plate and the incident light is introduced through the prism andis totally reflected and guided in the light guiding plate. Moreover,FIG. 31(c) shows a state in which the incident light is introduced fromthe end of the waveguide formed on a substrate into the waveguide and istotally reflected and guided in the waveguide.

[0005] The light guiding plate and the waveguide satisfy totalreflecting conditions in the light guiding plate and the waveguide byintroducing the incident light at a greater angle than a totalreflecting critical angle. Moreover, the light guiding plate and thewaveguide have been expected to be developed into various opticaldevices or optical systems which utilize a total reflection in thefuture.

[0006] As described above, in the conventional method of introducing theincident light into the light guiding plate and the waveguide, theincident light is introduced from the end face side of the light guidingplate and the waveguide or is introduced through the prism connected tothe end on either surface side of the light guiding plate. In the lightguiding plate and the waveguide which are thin and plate-shaped,however, the incidence opening area of the end face is small and acoupling efficiency with the incident light tends to be deteriorated.Moreover, the light guiding plate and the waveguide have been desired tohave a smaller thickness and a larger area, and the incidence openingarea of the end face tends to be reduced increasingly. Consequently,there is a fear that the coupling efficiency might be deteriorated.Furthermore, the shape of the incident light (a light source) and anintroducing position are restricted and the size and number of the lightsources is limited so that a light having a high output cannot beintroduced. Moreover, the incident light is to be beam-shaped or linearso that the type of the light source is restricted and an optical systemfor acquiring the shape described above is required.

[0007] In the case in which the reflector is a film having a metal or ametallic surface, moreover, an absorption is carried out at time of areflection so that a light loss is always caused. In the case of themultilayer film interference mirror, a transmitted light is present whenthe incidence angle of the incident light is increased. For this reason,it is impossible to obtain a perfect reflector having a high efficiencyfor an optional incidence angle.

DISCLOSURE OF THE INVENTION

[0008] The invention has been made in consideration of the conventionalproblems and has an object to provide an optical device which candirectly and efficiently introduce a planar incident light as it is andcan efficiently obtain a planar total reflected light on a desirableinterface without using a light guiding plate or an optical waveguide,and is constituted by a reflector having no absorption without dependingon an incidence angle.

[0009] In order to attain the object,

[0010] (1) the invention provides a planar optical device characterizedby such a feature that when an incident light is introduced like a planeinto the optical device, at least apart of the incident light thusintroduced is totally reflected by an interface of layers constitutingthe optical device, while the incident light is not substantiallyemitted from an opposite side to an incident light introduction side.

[0011] The optical device has a planar shape, and when the incidentlight is incident like a plane on the optical device, at least a part ofthe incident light thus introduced is totally reflected by the interfaceof the layers constituting the optical device and is returned to theincident light introduction side, and the incident light introduced inthe optical device is not substantially emitted from the opposite sideto the incident light introduction side. Consequently, the shape of theincident light, the introducing position and the type of a light sourceare not restricted but the planar incident light can be introduced likea plane directly and efficiently so that a planar total reflected lightcan be obtained efficiently on a desirable interface. Moreover, it ispossible to constitute a reflector having neither an incidence angledependency nor an absorption. Furthermore, a light is not substantiallytransmitted from the optical device. Therefore, it is possible toenhance a light utilization efficiency and to increase an applicationrange to an optical device and an optical system which utilize a totalreflection.

[0012] (2) The invention provides a planar optical device characterizedin that an optical element for changing an optical path is provided inthe optical device, and at least a part of a planar incident lightintroduced in the optical device is introduced into the optical elementfor changing an optical path and the substantially whole incident lightthus introduced is totally reflected by an interface of layersconstituting the optical device.

[0013] In the optical device, the optical element for changing anoptical path for the incident light is provided in the optical deviceand the incident light is introduced like a plane into the opticalelement for changing an optical path. The optical path for the planarincident light thus introduced is changed into a specific direction oran optional direction by the optical element for changing an opticalpath, and the substantially whole incident light is reflected through atotal reflection by the interface of the layers constituting the opticaldevice. Therefore, the shape of the incident light, the introducingposition and the type of a light source are not restricted but theplanar incident light can be introduced like a plane directly andefficiently so that the planar total reflected light can be obtainedefficiently on a desirable interface. Moreover, it is possible toconstitute a reflector having neither an incidence angle dependency noran absorption. Furthermore, a light is not substantially transmittedfrom the optical device. Therefore, it is possible to enhance a lightutilization efficiency and to increase an application range to anoptical device and an optical system which utilize a total reflection.

[0014] (3) The invention provides a planar optical device characterizedin that an optical element for selecting an optical path is provided inthe optical device, and at least a part of a planar incident lightintroduced in the optical device is introduced into the optical elementfor selecting an optical path and the substantially whole incident lightthus introduced is totally reflected through a total reflection by aninterface of layers constituting the optical device.

[0015] In the optical device, the optical element for selecting anoptical path for the incident light is provided in the optical deviceand the incident light is introduced like a plane into the opticalelement for selecting an optical path. The optical path for the planarincident light thus introduced is changed into a specific direction oran optional direction by the optical element for selecting an opticalpath, and the substantially whole incident light is reflected through atotal reflection by the interface of the layers constituting the opticaldevice. Therefore, the shape of the incident light, the introducingposition and the type of a light source are not restricted but theplanar incident light can be introduced like a plane directly andefficiently so that the planar total reflected light can be obtainedefficiently on a desirable interface. Moreover, it is possible toconstitute a reflector having neither an incidence angle dependency noran absorption. Furthermore, a light is not substantially transmittedfrom the optical device. Therefore, it is possible to enhance a lightutilization efficiency and to increase an application range to anoptical device and an optical system which utilize a total reflection.

[0016] (4) The invention provides a planar optical device characterizedin that an optical element for changing an optical path and an opticalelement for selecting an optical path are provided in this order from anincident light introduction side in a direction of a thickness of theoptical device, and when an incident light is introduced like a planeinto the optical element for changing an optical path, at least a partof the incident light thus introduced is introduced into the opticalelement for selecting an optical path and the substantially wholeincident light thus introduced is reflected through a total reflectionby an interface of layers constituting the optical device.

[0017] In the optical device, the optical element for changing anoptical path and the optical element for selecting an optical path areprovided in this order from the incident light introduction side in thedirection of the thickness of the optical device, and the incident lightis introduced like a plane into the optical element for changing anoptical path. The optical path for the incident light thus introduced ischanged into a specific direction or an optional direction by theoptical element for changing an optical path, and furthermore, only theincident light in the specific direction is transmitted by the opticalelement for selecting an optical path. Consequently, the substantiallywhole light introduced in the optical device is reflected through atotal reflection by the interface of the layers constituting the opticaldevice. Therefore, the shape of the incident light, the introducingposition and the type of a light source are not restricted but theplanar incident light can be introduced like a plane directly andefficiently so that the planar total reflected light can be obtainedefficiently on a desirable interface. Moreover, it is possible toconstitute a reflector having neither an incidence angle dependency noran absorption. Furthermore, a light is not substantially transmittedfrom the optical device. Therefore, it is possible to enhance a lightutilization efficiency and to increase an application range to anoptical device and an optical system which utilize a total reflection.

[0018] (5) The invention provides the optical device, wherein thesubstantially whole incident light which is reflected totally isreturned to the incident light introduction side of the optical device.

[0019] In the optical device, the substantially whole incident lightwhich is reflected totally is returned to the incident lightintroduction side of the optical device. In the medium having a totalreflecting surface, therefore, light guiding, storage and containmentare not substantially carried out.

[0020] (6) The invention provides the optical device, wherein the layerconstituting the optical device is not substantially absorbed into awavelength area of the incident light.

[0021] In the optical device, the layer constituting the optical deviceis not substantially absorbed into the wavelength area of the incidentlight. Therefore, it is possible to suppress the incident light and theloss of the incident light reflected totally, thereby obtaining anefficient optical device.

[0022] (7) The invention provides the optical device, wherein theoptical element for changing an optical path and the optical element forselecting an optical path are provided in optical contact with eachother.

[0023] In the optical device, the optical element for changing anoptical path and the optical element for selecting an optical path areprovided in optical contact with each other. Consequently, both lightcoupling properties can be enhanced. In addition, in the case in whichthe optical element for changing an optical path has a directivity, itis possible to introduce the incident light from the optical element forchanging an optical path into the optical element for selecting anoptical path with an incidence angle component held.

[0024] (8) The invention provides the optical device, wherein theoptical element for changing an optical path and the optical element forselecting an optical path are provided in optical contact with eachother through a medium having a greater refractive index than 1.

[0025] In the optical device, the optical element for changing anoptical path and the optical element for selecting an optical path areprovided in optical contact with each other through a medium having agreater refractive index than 1. Consequently, it is possible tointroduce the incident light from the optical element for changing anoptical path into the optical element for selecting an optical pathwithout generating a total reflection by an interface with the medium.

[0026] (9) The invention provides the optical device, further comprisinga transparent medium constituting a part of the optical device, theoptical element for changing an optical path being provided in a frontpart of an optical path of the transparent medium.

[0027] In the optical device, the incident light is transmitted throughthe transparent medium and is then introduced into the optical elementfor changing an optical path so that only the incident light in aspecific direction is transmitted.

[0028] (10) The invention provides the optical device, furthercomprising a transparent medium constituting a part of the opticaldevice, the optical element for selecting an optical path being providedin a front part of an optical path of the transparent medium.

[0029] In the optical device, the incident light is transmitted throughthe transparent medium and is then introduced into the optical elementfor selecting an optical path so that only the incident light in aspecific direction is transmitted.

[0030] (11) The invention provides the optical device, furthercomprising a transparent medium constituting a part of the opticaldevice, the optical element for changing an optical path and the opticalelement for selecting an optical path being provided in this order in afront part of an optical path of the transparent medium.

[0031] In the optical device, the incident light is transmitted throughthe transparent medium and is then introduced into the optical elementfor changing an optical path, and the optical path for the incidentlight is changed into a specific direction or an optional direction, andfurthermore, is introduced into the optical element for selecting anoptical path so that only the incident light in the specific directionis transmitted.

[0032] (12) The invention provides the optical device, wherein a mediumconstituting a part of the optical device is provided in a frontmostpart of the optical path of the optical device, and a front or rearinterface of an optical path for an incident light of the medium is setto be an interface generating the total reflection.

[0033] In the optical device, a medium constituting a part of theoptical device is provided in the frontmost part of the optical path ofthe optical device, and the incident light is totally reflected by thefront or rear interface of the optical path for the incident light ofthe medium.

[0034] (13) The invention provides the optical device, wherein, for theinterface generating the total reflection, a rear part of the opticalpath for the incident light is selected with na>nb if sin⁻¹ (nb/na)≦θ isset, and a front part of the optical path for the incident light isselected with na>nb if sin⁻¹ (1/na)<θ<sin⁻¹ (nb/na) is set, and thefront part of the optical path for the incident light is selected withna≦nb if sin⁻¹ (1/na)≦θ is set, in which nb represents a mean refractiveindex of the medium, na represents a mean refractive index of a layerprovided in the rear part of the optical path of the medium, and θrepresents an angle of a light advancing in the layer of the rear partof the optical path.

[0035] In the optical device, it is possible to control the interfacegenerating the total reflection by regulating the mean refractive indexof the medium for the mean refractive index of the layer in the rearpart of the optical path. Thus, it is possible to set a total reflectingsurface corresponding to the situation of use of the optical device.

[0036] (14) The invention provides the optical device, wherein theinterface generating the total reflection is set to be an interface of amedium having a first refractive index constituting a part of theoptical device and a medium provided in a front part of the optical pathfor the incident light in contact with the medium and having a secondrefractive index which is smaller than the first refractive index.

[0037] In the optical device, the total reflection is generated at apredetermined incidence angle based on a difference in a refractiveindex on the interface of the medium having the first refractive indexconstituting a part of the optical device and the medium provided in thefront part of the optical path for the incident light in contact withthe medium and having the second refractive index which is smaller thanthe first refractive index.

[0038] (15) The invention provides the optical device, wherein theinterface generating the total reflection is a frontmost surface of theoptical path for the incident light of the optical device.

[0039] In the optical device, the total reflection is generated on thefront most surface of the optical path for the incident light of theoptical device. In this case, the frontmost surface may be a thin layerhaving a low refractive index.

[0040] (16) The invention provides the optical device, wherein theinterface generating the total reflection has a forward side of theoptical path for the incident light to be an air contact interface.

[0041] In the optical device, the forward side of the optical path foran incident light comes in contact with a gas such as air or an inactive gas. Therefore, it is possible to generate the total reflectionwith a simple structure without providing a layer having a lowrefractive index which forms the total reflecting surface. Moreover, thefrontmost surface of the optical path for the incident light of theoptical device can be set to be the total reflecting surface.

[0042] (17) The invention provides the optical device, wherein theoptical element for changing an optical path includes and forwardoutputs a light having an angle θt to satisfy at least a condition ofsin θt>nw/nt, in which nt represents a mean refractive index of theoptical element for changing an optical path, nw represents a refractiveindex of a medium on a forward side of a total reflecting interface in afront part of the optical path, and θt represents an angle of a lightadvancing in a medium of the optical element for changing an opticalpath.

[0043] In the optical device, the light having an angle θt to satisfy atleast a condition of sin θt>nw/nt is transmitted through the opticalelement for changing an optical path and the optical path is changed tooutput the same light forward.

[0044] (18) The invention provides the optical device, wherein theoptical element for changing an optical path serves to change theoptical path by a refraction.

[0045] In the optical device, the optical element for changing anoptical path changes the optical path for the incident light by therefraction. Consequently, it is possible to introduce the incident lightinto the optical device without substantially reducing the intensity ofthe incident light.

[0046] (19) The invention provides the optical device, wherein theoptical element for changing an optical path is any of a lens array, aprism array and a heterorefractive index distribution member havingvarious refractive indices distributed.

[0047] In the optical device, it is possible to reduce the cost, and atthe same time, to display an excellent performance by properly selectingthe optical element including the lens array, the prism array or theheterorefractive index distribution member which is suitable for massproduction.

[0048] (20) The invention provides the optical device, wherein theoptical element for changing an optical path serves to change theoptical path by a diffraction.

[0049] In the optical device, the optical element for changing anoptical path changes the optical path for the incident light through adiffraction by a transmission type diffraction grating. Consequently,the incident light can be introduced into the optical device at anincidence angle with high precision.

[0050] (21) The invention provides the optical device, wherein theoptical element for changing an optical path is any of a volumehologram, a phase modulation type diffraction grating and an amplitudemodulation type diffraction grating.

[0051] In the optical device, mass transfer production can be carriedout by a photopolymer method or an injection molding method, forexample. Consequently, the cost of the optical device itself can bereduced.

[0052] (22) The invention provides the optical device, wherein theoptical element for changing an optical path serves to change an opticalpath by a light diffusion.

[0053] In the optical device, the optical element for changing anoptical path serves to change an optical path by the light diffusion.Consequently, the incident light can be incident on the optical devicein an optical direction.

[0054] (23) The invention provides the optical device, wherein theoptical element for changing an optical path is a porous member, aheterorefractive index distribution member, a dispersion member or adiffusion member having a concavo-convex surface.

[0055] In the optical device, it is possible to reduce the cost, and atthe same time, to display an excellent performance by properly selectingthe optical element to be the porous member, the heterorefractive indexdistribution member, the dispersion member or the diffusion member whichis suitable for mass production.

[0056] (24) The invention provides the optical device, wherein theoptical element for changing an optical path serves to change an opticalpath by a light reflection.

[0057] In the optical device, the optical element for changing anoptical path changes the optical path by the light reflection.Consequently, the incident light can be incident on the optical devicein an optional direction.

[0058] (25) The invention provides the optical device, wherein theoptical element for selecting an optical path has such a feature that asubstantially whole transmitted light which is emitted from the opticalelement has a greater angle component than a total reflecting criticalangle on an interface of layers in a front part of an optical path forthe incident light from the optical element for selecting an opticalpath or an interface in a front part of the optical path for theincident light of the optical element for selecting an optical path andincident lights having other angle components are selectively reflectedand are not transmitted.

[0059] In the optical device, the optical element for selecting anoptical path has such a feature that a substantially whole transmittedlight which is emitted from the optical element has a greater anglecomponent than a total reflecting critical angle on an interface oflayers in a front part of an optical path for the incident light fromthe optical element for selecting an optical path or an interface in afront part of the optical path for the incident light of the opticalelement for selecting an optical path and incident lights having otherangle components are selectively reflected by the optical element forselecting an optical path. Accordingly, only the incident light havingan incidence angle component to be reflected totally on the interface inthe front part of the optical path for the incident light is selectivelytransmitted through the optical element for selecting an optical path,and the incident light having such an incidence angle component as notto be reflected totally is not transmitted.

[0060] (26) The invention provides the optical device, wherein theoptical element for selecting an optical path transmits a substantiallywhole light having an angle θs to satisfy a condition of sin θs>nw/ns,in which ns represents a mean refractive index of the optical elementfor selecting an optical path, nw represents a refractive index of amedium on a forward side of a total reflecting interface in a front partof the optical path, and θs represents an angle of a light advancing inthe medium of the optical element for selecting an optical path.

[0061] In the optical device, the substantially whole light having anangle Os to satisfy a condition of sin θs>nw/ns is transmitted throughthe optical element for selecting an optical path and other lights arereflected. Consequently, only a specific light component is selectivelytransmitted.

[0062] (27) The invention provides the optical device, wherein theoptical element for selecting an optical path has a function ofselectively carrying out a reflection for a wavelength area of anincident light, and a wavelength of the incident light to be reflectedselectively is shifted toward a short-wavelength side when an incidenceangle of the incident light on the optical element for selecting anoptical path is reduced with respect to a surface of the opticalelement.

[0063] In the optical device, the optical element for selecting anoptical path has the function of selectively carrying out a reflectionfor the wavelength area of the incident light, and the wavelength of theincident light to be reflected selectively is shifted toward theshort-wavelength side when the incidence angle of the incident light onthe optical element is reduced with respect to the surface of theoptical element. By utilizing such a property, it is possible to designthe optical element for selecting an optical path such that only anincident light having a predetermined incidence angle component istransmitted, thereby selectively extracting only an incident lighthaving an incidence angle component generating a total reflection.

[0064] (28) The invention provides the optical device, wherein when anincidence angle of the incident light on a total reflecting interface ina front part of an optical path for the incident light in the opticalelement for selecting an optical path is equal to or smaller than atotal reflecting critical angle, the optical element for selecting anoptical path selectively reflects the substantially whole incidentlight.

[0065] In the optical device, when the incidence angle of the incidentlight on the optical element for selecting an optical path and anincidence angle on the total reflecting interface in the front part ofthe optical path for the incident light to be changed depending on therefraction conditions of each layer are equal to or smaller than thetotal reflecting critical angle on the total reflecting interface, theoptical element for selecting an optical path selectively reflects thesubstantially whole incident light. Consequently, the incident lighthaving such an angle component as not to be reflected totally isselectively reflected over the total reflecting interface and is nottransmitted forward in the optical path.

[0066] (29) The invention provides the optical device, wherein theoptical element for selecting an optical path is a light interferencefilter including a dielectric multilayer film.

[0067] In the optical device, it is possible to form an optionalwavelength selecting reflective film with a large area and a simplestructure by using the light interference filter including thedielectric multilayer film. By utilizing the incidence angle dependencyof the reflecting wavelength, it is possible to easily form the opticalelement for selecting an optical path.

[0068] (30) The invention provides the optical device, wherein theoptical element for selecting an optical path is a Bragg reflectingfilter including a cholesteric liquid crystal and a volume hologram.

[0069] In the optical device, it is possible to form the optical elementfor selecting an optical path at a low cost by using the Braggreflecting filter including the cholesteric liquid crystal and thevolume hologram.

[0070] (31) The invention provides a planar optical device characterizedin that an optical element for introducing an incident light is providedin the optical device, and when the incident light is introduced like aplane into the optical element for introducing the incident light, thesubstantially whole incident light thus introduced is reflected througha total reflection by an interface of layers constituting the opticaldevice.

[0071] In the optical device, the optical element for introducing theincident light to be reflected totally by the interface of the layersconstituting the optical device is provided in the optical device, andthe incident light is introduced like a plane into the optical elementfor introducing the incident light. The substantially whole incidentlight thus introduced is reflected through a total reflection by theinterface of the layers constituting the optical device. Consequently,it is possible to exactly introduce the planar incident light directlyand efficiently with a simple structure without introducing the incidentlight from the end face of the optical device at a greater angle thanthe total reflecting critical angle and to increase the output of theoptical device. Moreover, since the substantially whole incident lightthus introduced is reflected by the total reflection having noreflection loss, the optical device can be caused to function as areflector having a high efficiency.

[0072] (32) The invention provides the optical device, wherein theoptical element for introducing an incident light is a prism arrayarranged like a plane.

[0073] In the optical device, the planar incident light in apredetermined direction is converted to have such an angle as togenerate the total reflection in the optical device by the prism array.Consequently, it is possible to introduce the incident light to bereflected totally into the optical device.

[0074] (33) The invention provides the optical device, wherein theincident light is a collimated light ranging within a specific incidenceangle.

[0075] In the optical device, the incident light is the collimated lightranging within the specific incidence angle. Consequently, it ispossible to supply the incident light having a specific incidence anglecomponent to the optical device, thereby enhancing a light utilizationefficiency.

[0076] (34) The invention provides the optical device, wherein theincident light is a collimated light having a plurality of incidenceangles.

[0077] In the optical device, the incident light is the collimated lighthaving a plurality of incidence angles. Therefore, the incident lighthaving a plurality of incidence angle components can be supplied to theoptical device at a time.

[0078] (35) The invention provides the optical device, wherein theincident light is a diffused light having an optional incidence angle.

[0079] In the optical device, the incident light is the diffused lighthaving an optional incidence angle. Consequently, the incident light canbe introduced into the optical device in various directions so that theuniformity of the incident light can be enhanced.

[0080] (36) The invention provides the optical device, wherein a lightsource is provided in the optical device and the incident light isemitted from the light source.

[0081] In the optical device, the light source is provided in theoptical device. Consequently, a light emitted from the light source canbe directly introduced into the optical device so that a loss canconsiderably be reduced during the introduction of the incident light.

[0082] (37) The invention provides the optical device, wherein theincident light is incident from an outside of the optical device.

[0083] In the optical device, the incident light is introduced from theoutside of the optical device. Consequently, the degree of freedom of adesign of the optical device can be enhanced and a large-sized lightsource can also be utilized so that an output can easily be increased.

[0084] (38) The invention provides the optical device, wherein areflector for transmitting, toward the optical device side again, alight which is once incident on the optical device and is reflected bythe optical device is provided opposite to an incident lightintroduction side of the optical device.

[0085] In the optical device, the reflector is provided opposite to theincident light introduction side of the optical device. Consequently,the light which is once incident on the optical device and is reflectedby the optical device is irradiated on the reflector, and furthermore,the light reflected by the reflector is transmitted again toward theoptical device side. Consequently, the light is recycled so that a lightutilization efficiency can be enhanced and an increase in the efficiencycan be obtained.

[0086] (39) The invention provides the optical device, wherein theincident light is any of a UV light, a visible light and an infraredlight.

[0087] In the optical device, the incident light is set into thewavelength area of any specific band of the UV light, the visible lightand the infrared light. Consequently, the incident light can reliably betransmitted or reflected selectively in the optical device.

[0088] (40) The invention provides the optical device, wherein theincident light is emitted from any of a discharge lamp, a laser beamsource, an LED, an inorganic or organic EL, an incandescent lamp, acathode-ray lamp and an FED.

[0089] In the optical device, the incident light is emitted from thedischarge lamp so that a light source to be used generally can beutilized as it is, the incident light is emitted from the laser beamsource so that a collimated light can easily be obtained, the incidentlight is emitted from the LED so that a cost can be reduced and a lightemitting wavelength area can be preset, the incident light is emittedfrom the inorganic or organic EL so that planar light emission isobtained, the incident light is emitted from the incandescent lamp sothat an optional wavelength component can be fetched by filtering toanswer the purpose, and the incident light is emitted from thecathode-ray lamp or the FED so that a planar light can be obtaineddirectly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0090]FIG. 1 is a view showing a schematic structure according to afirst embodiment of an optical device according to the invention.

[0091] FIGS. 2(a) to 2(c) show the views showing a transmission typediffraction grating, 2(a) showing a volume hologram, 2(b) showing arelief type diffraction grating and 2(c) showing a refractive indexmodulation type diffraction grating.

[0092] FIGS. 3(a) to 3(c) show the views showing a light diffusion and alight diffusing plate utilizing the light diffusion, 3(a) showing aporous member, 3(b) showing a heterorefractive index dispersion memberand distribution member in which materials having different refractiveindices are distributed and dispersed, and 3(c) showing a lightdiffusion member having a concavo-convex surface.

[0093]FIG. 4 is a view showing the layer structure of a lightinterference filter.

[0094]FIG. 5 is a view for explaining the optical property of theoptical device.

[0095]FIG. 6 is a view collectively showing the configuration of anincident light.

[0096]FIG. 7 is a view showing the incidence angle of a light incidenton the optical element for selecting a light.

[0097]FIG. 8 is a graph showing, for each incidence angle, the spectraltransmittance of the optical element for selecting an optical path withrespect to the wavelength of the incident light.

[0098] FIGS. 9(a) and 9(b) show the views showing an optical path in theoptical element for selecting an optical path.

[0099]FIG. 10 is a view showing an example in which the optical elementfor selecting an optical path is constituted by a liquid crystal film.

[0100] FIGS. 11(a) to 11(f) show the graphs showing, for each incidenceangle, a spectral transmittance obtained by the optical element forselecting an optical path in FIG. 10 with respect to the wavelength ofthe incident light.

[0101]FIG. 12 is a view showing the structure of an optical deviceaccording to a variant of the first embodiment.

[0102]FIG. 13 is a view showing the structure of an optical deviceaccording to a second embodiment.

[0103]FIG. 14 is a view showing the structure of an optical deviceaccording to a third embodiment.

[0104]FIG. 15 is a view showing a difference in an optical path for anincidence angle in the case in which a refractive index of a transparentmedium is smaller than a refractive index n3 of the optical element forselecting an optical path.

[0105]FIG. 16 is a view showing the difference in an optical path forthe incidence angle in the case in which the refractive index of thetransparent medium is equal to or greater than that of the opticalelement for selecting an optical path.

[0106]FIG. 17 is a view showing the structure of an optical deviceaccording to a fourth embodiment.

[0107]FIG. 18 is a view showing the structure of an optical deviceaccording to a fifth embodiment.

[0108]FIG. 19 is a view showing the structure of an optical deviceaccording to a sixth embodiment.

[0109]FIG. 20 is a view showing the structure of an optical deviceaccording to a seventh embodiment.

[0110]FIG. 21 is a view showing the structure of an optical deviceaccording to a variant of the seventh embodiment.

[0111]FIG. 22 is a view showing the structure of an optical deviceaccording to an eighth embodiment.

[0112] FIGS. 23(a) and 23(b) show the views showing the structure of anoptical device according to a ninth embodiment.

[0113]FIG. 24 is a view showing the structure of an optical deviceaccording to a tenth embodiment.

[0114]FIG. 25 is a view showing the conceptual whole structure of theoptical device in FIG. 24.

[0115]FIG. 26 is a view showing the structure of an optical deviceaccording to an eleventh embodiment.

[0116]FIG. 27 is a view showing an example of a structure of the opticaldevice according to the invention.

[0117]FIG. 28 is a graph showing the wavelength band of an incidentlight.

[0118] FIGS. 29(a) to 29(c) show the graphs showing a change in aspectral transmittance for a wavelength every incidence angle.

[0119] FIGS. 30(a) to 30(c) show the graphs showing the spectraltransmittance for the incidence angle every wavelength.

[0120] FIGS. 31(a) to 31(c) show the views showing a state in which anincident light is introduced from a general light guiding plate andwaveguide according to the conventional art.

[0121] In the drawings, 10 denotes an optical element for changing anoptical path, 12 denotes an optical element for selecting an opticalpath, 14 denotes a transparent medium, 16 denotes a transparent medium(air), 20 denotes a substance having a different refractive index, 22denotes an interface, 26 denotes a transparent electrode, 28 denotes anoriented layer, 30 denotes a cholesteric liquid crystal layer, 32denotes an intermediate transparent medium, 34 and 35 denote atransparent medium, 36 denotes an optical connecting medium, 38 denotesa medium, 40 denotes a reflector, 42 denotes a light source, 44 denotesa transparent base material, 46 denotes a transmission type refractivegrating, 48 denotes a medium, 50 denotes a microprism array, 52 denotesa total reflecting surface, 54 denotes a prism, 56 denotes a transparentmedium, 58 denotes a total reflecting surface, 60 denotes a transparentbase material, 62 denotes a transmission type diffraction grating, 100,200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200 and 1300 denotean optical device, A and B denote an optical path, n denotes arefractive index (a mean refractive index), n1 denotes a refractiveindex of the transparent medium 14, n2 denotes a refractive index of thetransparent medium 16, n3 denotes a refractive index of the opticalelement 12, n4 denotes a refractive index of the transparent medium 34,n5 denotes a refractive index of the medium 38, n7 denotes a refractiveindex of the microprism array 50, n8 denotes a refractive index of thetransparent medium 56, ne denotes an extraordinary index, no denotes anordinary index, P denotes a spiral pitch, T denotes a spectraltransmittance, α denotes a vertical angle, Δn denotes a doublerefractive index, Δλ denotes a reflecting wavelength width, θ, θ₀, θ₁,θ₂ and θ₃ denote an incidence angle, θ_(C) denotes a total reflectingcritical angle, and λ denotes a wavelength.

BEST MODES FOR CARRYING OUT THE INVENTION

[0122] Preferred embodiments of an optical device according to theinvention will be described below in detail with reference to thedrawings.

[0123]FIG. 1 shows a schematic structure according to a first embodimentof the optical device of the invention. An optical device 100 accordingto the embodiment has a multilayer structure in which an optical element10 for changing an optical path, an optical element 12 for selecting anoptical path and a transparent medium 14 are provided in this order fromthe introduction side of an incident light. A transparent medium 16 ispresent in the front part of the optical path of the transparent medium14 in the optical device 100, and the relationship between a refractiveindex n1 (a first refractive index) of the transparent medium 14 and arefractive index n2 (a second refractive index) of the transparentmedium 16 is set to satisfy total reflecting conditions on an interface22 of the transparent medium 14 and the transparent medium 16. Morespecifically, the transparent medium 14 can be constituted by a glasssubstrate (n1=1.5) and the transparent medium 16 can be constituted asair (n2=1.0), for example. Each layer constituting the optical device100 is not substantially absorbed into the wavelength area of theincident light but suppresses the incident light and the loss of theincident light which is totally reflected by the interface 22, therebyconstituting an optical device having a high efficiency.

[0124] The optical element 10 for changing an optical path serves tochange the optical path by utilizing a refraction, a diffraction, alight diffusion and a light reflection, and the following kinds ofoptical elements can be used as an example. In the case in which therefraction is to be utilized, a lens array, a prism array and arefractive index dispersion member can be used and the intensity of theincident light is not reduced substantially. In the case in which thediffraction is to be utilized, a transmission type diffraction gratingshown in FIG. 2 is used, and a phase modulation type diffraction gratingsuch as a volume hologram (see FIG. 2(a)), a relief type diffractiongrating (see FIG. 2(b)) or a refractive index modulation typediffraction grating (see FIG. 2(c)) and an amplitude modulation typediffraction grating can be used to set the angle of an optical path foran incident light with high precision. Each optical element can bemass-transferred and produced by a photopolymer method or an injectionmolding method, for example.

[0125] In the case in which the light diffusion is to be utilized,moreover, a light diffusing plate shown in FIG. 3 is used and examplesthereof include a porous member (see FIG. 3(a)), a heterorefractiveindex distribution member and dispersion member in which a material 20having a different refractive index is distributed and dispersed (seeFIG. 3(b)), and a light diffusion member or scattering member having aconcavo-convex surface (see FIG. 3(c)). In the case in which the lightreflection is to be utilized, a distribution member of a microreflectorto carry out a reflection in an optional direction is used. Any opticalelement is suitable for mass production so that a cost can easily bereduced.

[0126] In the optical element 12 for selecting an optical path, thesubstantially whole selected and transmitted light emitted from theoptical element 12 has a greater angle component than a total reflectingcritical angle in a layer provided in the front part of an optical pathfor an incident light, and incident lights having other angle componentsare selectively reflected and are not transmitted. More specifically,only an incident light having a greater angle component than a totalreflecting critical angle θ_(C) to be such a condition as to generate atotal reflection on an interface of the transparent medium 14 and thetransparent medium 16 is transmitted through the optical element 12 forselecting an optical path and incident lights having other anglecomponents are shielded. The total reflecting critical angle θ_(C) iscalculated by an equation (1).

θ_(C)=sin⁻¹(n2/n1)  (1)

[0127] Specific examples of the optical element 12 for selecting anoptical axis include a light interference filter comprising a dielectricmultilayer film. FIG. 4 shows the layer structure of the lightinterference filter.

[0128] The light interference filter is a dielectric multilayer filmconstituted by sequentially providing TiO₂ and SiO₂, and an opticalcharacteristic thereof has the function of selectively reflecting anincident light based on a wavelength thereof which will be describedbelow in detail, and has such a characteristic that a wavelength to beselectively reflected depending on an incidence angle is shifted towardthe short-wavelength side. When the wavelength area of the incidentlight is represented by λ_(iS) to λ_(iL) (λ_(iS)<λ_(iL)), allsubstantial incident lights having the wavelength areas λ_(iS) to λ_(iL)are selectively reflected for a light including an angle componenthaving the output angle of the selected and transmitted light emittedfrom the optical element 12 which is equal to or smaller than the totalreflecting critical angle θ_(C). According to the structure, an optionalwavelength selecting reflective film can be formed with a large area anda simple structure, and the optical element 12 for easily selecting anoptical path can be formed by utilizing the incidence angle dependencyof the reflection wavelength. The light interference filter may be ametal/dielectric multilayer film in which a metal film is added to thelayer structure of the dielectric multilayer film. The lightinterference filter comprising the dielectric multilayer film can beformed by providing, as films, a plurality of thin film materials on atransparent support substrate by EB evaporation (electron beamcoevaporation) or sputtering. Moreover, the thin film material may be anorganic multilayer film having a different refractive index or anorganic multilayer film containing an inorganic matter, and can beformed at a lower cost by coating or laminating in this case.

[0129] Detailed description will be given to the optical element forchanging an optical path and the optical property of the optical elementfor selecting an optical path.

[0130] First of all, there will be supposed the case in which theoptical element for changing an optical path serves to change theoptical path by a refraction, for example. As shown in FIG. 5, in thecase of an optical device in which an optical element for changing anoptical path (a mean refractive index nt), an optical element forselecting an optical path (a mean refractive index ns), a transparentmedium u (a mean refractive index nu), a transparent medium v (a meanrefractive index nv), and a transparent medium w on the forward side ofa total reflecting surface (a mean refractive index nw) are provided inthis order, the relationship between an incidence angle on eachinterface and the mean refractive index of each medium is represented asfollows if the interface of the transparent medium v and the transparentmedium w is a total reflecting surface.

nv·sin θv=nw

nu·sin θu=nv·sin θv=nw

ns·sin θs=nu·sin θu=nw

nt·sin θt=ns·sin θs=nw

[0131] wherein θt, θs, θu and θv represent an optical path angle in eachmedium. Accordingly, it is necessary to include at least a light havingan angle θt to satisfy the following condition as the condition of theoptical element for changing an optical path and to output the light ina forward direction.

sin θt>nw/nt

[0132] Preferably, the light having the angle θt to satisfy thecondition is included as much as possible and is output in the forwarddirection. If the transparent medium w is air, nw=1 is obtained and thecondition described above is set as follows.

sin θt>1/nt

[0133] On the other hand, the condition of the optical element forselecting an optical path is set to transmit only a light satisfying thefollowing condition.

sin θs>nw/ns

[0134] If the transparent medium w is the air, nw=1 is obtained and thecondition described above is set as follows.

sin θs>1/ns

[0135] A light to be irradiated like a plane is used for an incidentlight on the optical device 100, and any of a collimated light and adiffused light can be used. Moreover, the light may be incident from theoutside of the optical device and may be incident to have a light sourcetherein. In the case of the collimated light, an incident light having aspecific incidence angle component can be supplied to the optical device100 and a light utilization efficiency can be enhanced. On the otherhand, in the case of the diffused light, the incident light can beintroduced into the optical device 100 in various directions and anoptional plane light source taking a low cost can be used. In the casein which a light source is provided on the inside, moreover, a lightemitted from the light source is directly introduced into the opticaldevice 100 and the optical device and the light source can be formedintegrally so that a size and a thickness can be reduced and a lightintroduction efficiency can be enhanced. On the other hand, in the casein which the light source is provided on the outside, the degree offreedom of a design of the optical device 100 can be enhanced and anoptional external plane light source having a large size can also beutilized so that an output can easily be increased.

[0136]FIG. 6 collectively shows the configurations of the incidentlight. As shown in FIG. 6, it is possible to use, for the incidentlight, a collimated light ranging within a specific incidence angle orhaving one or more incidence angles or a diffused light to be anincident light in an optional direction. Moreover, it is possible touse, for each of the collimated light and the diffused light, a lightwhich is incident like a plane from the outside of the optical device inthe front part of the optical path of the optical device using theoptical device and the light source separately or a light which isintegrated in such a state as to provide a light source in the frontpart of the optical path of the optical device and is incident like aplane.

[0137] It is possible to use, for the incident light, a light having awavelength in a specific band, for example, a UV light, a visible lightsuch as a blue light or a green light, and an infrared light. In thecase in which the infrared light is used, particularly, the effect ofblocking a heat wave can also be obtained. Therefore, it is possible toobtain a convenience such as the prevention of overheat in respect ofpractical use.

[0138] For the type of the light source, moreover, it is possible to usea discharge lamp which is generally used and can be exactly utilized,for example, a fluorescent lamp, a mercury lamp, a neon tube lamp or aCrookes tube to be an electronic tube which is charged with an inactivegas or a mercury vapor, a laser beam source from which a collimatedlight can easily be obtained, an LED which is inexpensive and has adefined wavelength area, an inorganic or organic EL from which a planarlight can be obtained, an incandescent lamp capable of fetching anoptical wavelength component by emitting and filtering a white light toanswer the purpose, a cathode-ray lamp to be a cathode-ray display tubesuch as a CRT from which a planar light to be introduced into theoptical device can be directly obtained and an FED (field emissiondisplay) to be a planar display tube from which a planar light can bedirectly obtained.

[0139] Next, the characteristic of the optical element 12 for selectingan optical path will be described in detail with reference to FIGS. 7 to9.

[0140]FIG. 7 shows the incidence angle of a light which is incident onthe optical element 12, FIG. 8 is a graph showing, for each incidenceangle, the spectral transmittance of the optical element 12 for thewavelength of an incident light, and FIG. 9 is a view showing an opticalpath on the inside and outside of the optical element 12.

[0141] First of all, there will be supposed the case in which a light isincident on the optical element 12 at incidence angles θ₀, θ₁, θ₂ and θ₃as shown in FIG. 7. As shown in FIG. 8, the spectral transmittance ofthe optical element 12 is changed. More specifically, if the incidenceangle is represented by θ₀ (zero degree) which is equal to or smallerthan a total reflecting critical angle θ_(C), the spectral transmittanceis approximately 0% with respect to the wavelength areas λ_(iS) toλ_(iL) of the incident light so that a light shielding state (in which alight is not transmitted but reflected) is brought. On the other hand,if the incidence angle is greater than the total reflecting criticalangle θ_(C), the transmitting characteristic of the spectraltransmittance is shifted toward the short-wavelength side so that theamount of a transmitted light is increased when the incidence angle isincreased in order of θ₁, θ₂ and θ₃. In other words, when the incidenceangle of the light incident on the optical element 12 for selecting anoptical path is reduced with respect to the surface of the opticalelement 12, the wavelength of the incident light which is selectivelyreflected is shifted toward the short-wavelength side. Consequently, alight having an incidence angle component θ₀ of the incident light isnot transmitted and lights having greater incidence angle components θ₁,θ₂ and θ₃ than a specific angle are transmitted with an increase in anamount in this order. Therefore, the optical element 12 is designed tohave such a spectral characteristic that only a greater incident lightcomponent than a total reflecting critical angle θ_(C) on apredetermined interface is transmitted. Consequently, an incident lightcomponent which does not satisfy total reflecting conditions can beshielded and only an incident light component for a total reflection canbe selectively emitted from the optical element 12.

[0142] With reference to FIG. 9, description will be given to an opticalpath for an incident light in the case in which the optical device 100is constituted by using the optical element 12 designed to transmit onlya greater incident light component than the total reflecting criticalangle θ_(C) on the interface 22 as mentioned above.

[0143]FIG. 9(a) shows an optical path A in which a light incident on theoptical element 12 for selecting an optical path is reflected by theoptical element 12, and an optical path B in which the light incident onthe optical element 12 for selecting an optical path is transmittedthrough the optical element 12 and is totally reflected by the interface22 of the transparent medium 14 and the transparent medium 16 providedin the front part of the optical path.

[0144] The optical path A is used when an incidence angle θ_(i) of theincident light is equal to or smaller than the total reflecting criticalangle θ_(C) on the interface 22, and the optical element 12 does nottransmit a light having the incidence angle component but selectivelyreflects the same light by a surface thereof. For this reason, the lighthaving an incidence angle component which is equal to or smaller thanthe total reflecting critical angle θ_(C) is shielded against the frontpart of the optical path by means of the optical element 12.

[0145] The optical path B is used when the incidence angle θ_(i) of theincident light is greater than the total reflecting critical angle θ_(C)on the interface 22, and the optical element 12 transmits a light havingthe incidence angle component. For this reason, the light having agreater incidence angle component than the total reflecting criticalangle θ_(C) is transmitted through the optical element 12 and isintroduced into the transparent medium 14, and is totally reflected bythe interface 22.

[0146]FIG. 9(a) shows the case in which a refractive index na on theside on which the light is incident and a refractive index nb of thetransparent medium 14 are equal to each other, and the incidence angleθ_(i) for the optical element 12 and the angle θ_(S) on the interface 22are equal to each other.

[0147] On the other hand, FIG. 9(b) shows the case in which therefractive index na on the side on which the light is incident and therefractive index nb of the transparent medium 14 are different from eachother, and the incidence angle θ_(i) for the optical element 12 and theincidence angle θ_(S) on the interface 22 are different from each other.In this case, the optical element 12 is designed such that the incidenceangle θ_(S) on the interface 22 is greater than the total reflectingcritical angle θ_(C).

[0148] The optical device 100 is constituted by using the opticalelement 12 for selecting an optical path which is designed as describedabove. Consequently, when a planar incident light comprising thecollimated light or the diffused light introduced from the inside oroutside of the optical device 100 is incident on the optical element 10for changing an optical path as is indicated by an optical path shown inan arrow of FIG. 1, the optical path is changed through a diffusion fromthe irradiation position of the light. When a light having an opticalpath changed reaches the optical element 12 for selecting an opticalpath, only the incident light having a greater angle component than thetotal reflecting critical angle θ_(C) on the interface 22 of thetransparent medium 14 and the transparent medium 16 is transmittedthrough the optical element 12 and incident lights having other anglecomponents are reflected by the surface of the optical element 12 towardthe light incident side.

[0149] Accordingly, only a light to be reflected totally by theinterface 22 of the transparent medium 14 and the transparent medium 16which is incident on the optical device 100 is introduced into the frontpart of the optical path, and the light thus introduced is totallyreflected by the interface 22 to be a face in the frontmost part of theoptical path for the incident light in the optical device 100. Morespecifically, in the optical element 12 for selecting an optical path,the substantially whole transmitted light emitted from the opticalelement 12 has a greater angle component than a total reflectingcritical angle on an interface in the front part of the optical path forthe incident light of the interface of layers provided in the front partof the light path for the incident light through the optical element 12for selecting an optical path, and incident lights having other anglecomponents are selectively reflected and are not transmitted. In amedium having a total reflecting surface, light guiding, storage andcontainment are not substantially carried out.

[0150] Moreover, a part of the light reflected toward the light incidentside by the surface of the optical element 12 for selecting an opticalpath is reflected at the light incident side of the optical element 10for changing an optical path, and is transmitted into the opticalelement 12 for selecting an optical path again. The light thustransmitted again has an incidence angle increased to be greater thanthe total reflecting critical angle θ_(C), and is thus transmittedthrough the optical element 12 and is introduced into the transparentmedium 14.

[0151] According to the optical device 100 in accordance with theembodiment, thus, the incident light is directly and efficientlyintroduced like a plane from the planar light source into the opticaldevice 100 without using a light guiding plate or an optical waveguide.As compared with the case in which the light is incident from the endface side, therefore, an introduction port for the incident light can beconsiderably enlarged and a coupling efficiency with the incident lightcan be enhanced so that a planar total reflected light can be obtainedefficiently without an influence by a reduction in the thickness of theoptical device 100 itself. Moreover, an increase in the output of theoptical device 100 can be achieved easily. Furthermore, at least a partof the incident light introduced into the optical device by a reflectorhaving no absorption without depending on an incidence angle isreflected by a total reflection having no reflection loss. Therefore,the optical device can be caused to function as a reflector having ahigh efficiency. Since a part of the incident light reflected by eachinterface in the optical device is transmitted again into the front partof the optical path, and furthermore, the light transmitted from theoptical device is not substantially generated, a light utilizationefficiency can be enhanced. Consequently, it is possible to increase anapplication range to an optical device and an optical system whichutilize the total reflection of the optical device. A gas contactinterface on which the optical device 100 comes in contact with air(which may be an inactive gas) is set to be a total reflecting surfaceso that the total reflection can be generated with a simple structurewithout separately providing a layer having such a refractive index asto generate the total reflection.

[0152] In the embodiment, moreover, the optical element for changing anoptical path is provided in optical contact with the optical element forselecting an optical path. Therefore, both light coupling properties canbe enhanced. In addition, in the case in which the optical element forchanging an optical path has a directivity, the incident light can beintroduced from the optical element for changing an optical path intothe optical element for selecting an optical path with the incidenceangle component held.

[0153] Next, description will be given to another example of a structurein which a Bragg reflecting filter is used as the optical element 12 forselecting an optical path in place of the light interference filter.

[0154]FIG. 10 shows an example in which the optical element 12 forselecting an optical path is constituted by a liquid crystal film. Inthis case, the optical element 12 is constituted by a pair oftransparent electrodes 26 comprising ITO, an oriented layer 28 formed onthe inside thereof, and a cholesteric liquid crystal layer 30 surroundedby the oriented layer 28.

[0155] The filtering effect of the cholesteric liquid crystal layer 30having such a structure will be described below. The cholesteric liquidcrystal layer 30 has a cholesteric liquid crystal molecule oriented inparallel with a layer, and presents a spiral structure in the verticaldirection to the layer.

[0156] A double refractive index Δn can be expressed in an equation (2),wherein an ordinary index, an extraordinary index, a double refractiveindex and a mean refractive index in the cholesteric liquid crystallayer 30 are represented by no, ne, Δn and n, respectively.

Δn=ne−no  (2)

[0157] Moreover, the mean refractive index n is approximately expressedin an equation (3).

n=(ne+no)/2  (3)

[0158] Furthermore, in the case in which the spiral pitch of thecholesteric liquid crystal layer 30 is represented by P [nm], thecholesteric liquid crystal layer 30 indicates such a characteristic asto selectively carry out a reflection in the principle of a Braggreflection. More specifically, in the case in which a light incident onthe cholesteric liquid crystal layer 30 at an incidence angle θ [deg] isselectively reflected, a central wavelength λ(θ) [nm] of the incidentlight can be expressed in an equation (4).

λ(θ)=(0)·cos [sin⁻¹(sin θ/n)]  (4)

[0159] The incident light is incident from air (a refractive index=1).The λ(0) [nm] represents a central wavelength with an incidence angleθ₀, that is, when the light is incident vertically to a layer, and canbe expressed in an equation (5).

λ(0)=n·P  (5)

[0160] Moreover, a reflection wavelength width Δλ [nm] can be expressedin an equation (6).

Δλ=Δn·P  (6)

[0161] Accordingly, the ordinary index no, the extraordinary index neand the spiral pitch P which are the physical property values of thecholesteric liquid crystal layer 30 are controlled to form a layer.Consequently, it is possible to form an optical filter having anoptional reflecting central wavelength λ(θ) to be changed depending onthe incidence angle θ and a desirable reflecting wavelength width Δλ.For example, the spiral pitch P can be regulated by a manufacturingmethod for mixing and preparing at least two kinds of materials havingdifferent spiral pitches.

[0162] In the case in which the wavelength area of an incident light tobe an object is large, furthermore, it is also necessary to enlarge theselecting reflection wavelength area of the cholesteric liquid crystallayer. In this case, it is possible to enlarge the reflecting wavelengtharea by orienting a liquid crystal in such a manner that the spiralpitch is continuously varied in the direction of a thickness. Moreover,it is also possible to enlarge the reflecting wavelength area bylaminating the cholesteric liquid crystal layers in the differentselecting reflection wavelength areas.

[0163] The cholesteric liquid crystal layer 30 can be manufactured inthe following manner.

[0164] A polyimide oriented film is coated on a support member forforming a cholesteric liquid crystal and is then dried, and a surfacetreatment is carried out by rubbing. Consequently, the polyimideoriented film is formed. The polyimide oriented film is coated with aprepared solution having a mixture of a low molecular cholesteric liquidcrystal or a nematic liquid crystal and a chiral agent causing a twist,a polymeric monomer and a photopolymerization initiator which are mixedwith an organic solvent, and orientation is then carried out at a propertemperature. Thereafter, an ultraviolet radiation is exposed to anecessary portion and is photopolymerized, and an unnecessary portion isremoved by a development. Finally, high temperature baking is carriedout to obtain a stabilization.

[0165] In order to control the direction of the twist and the reflectingincidence angle, it is preferable that the cholesteric liquid crystal,the chiral agent and each concentration should be changed appropriately.

[0166] Moreover, it is also possible to form a film by using a polymericcholesteric liquid crystal. In this case, in the same manner asdescribed above, the polyimide oriented film is coated with a preparedsolution in which a polymeric cholesteric liquid crystal and aphotopolymerization initiator are mixed with an organic solvent and anorientation is then carried out at a proper temperature, and anultraviolet radiation is exposed to a necessary portion and isphotopolymerized. A reflecting incidence angle can be controlled byproperly selecting an orientation temperature and a stabilization can beobtained by the photopolymerization.

[0167]FIG. 11 shows the spectral transmittance of the optical element 12for selecting an optical path having the structure described above. Inthis example, a cholesteric liquid crystal layer is obtained bysuperposing a left twisted cholesteric liquid crystal layer and a righttwisted liquid crystal layer and a total polarizing component isreflected in a reflection wavelength area. In the case in which theincidence angle is represented by θ₀ which is equal to or smaller thanthe total reflecting critical angle θ_(C) (see FIG. 7), the spectraltransmittance is approximately 0% with respect to the wavelength areasλ_(iS) to λ_(iL) of the incident light so that a light shielding stateis brought. When the incidence angle is greater than the totalreflecting critical angle θ_(C) and is increased in order of θ₁, θ₂ andθ₃, the transmitting characteristic of the spectral transmittance isshifted toward the short-wavelength side so that the amount of atransmitted light is increased. Consequently, an incident light havingan incidence angle component θ₀ is not transmitted but lights havingincidence angle components θ₁, θ₂ and θ₃ which are greater than aspecific angle are transmitted with an increase in an amount in thisorder. By carrying out a design to have the spectral characteristic ofthe optical element 12 such that only a greater incident light componentthan the total reflecting critical angle θ_(C) on a predeterminedinterface is transmitted, an incident light component which does notsatisfy total reflecting conditions can be removed selectively and onlyan incident light component to be totally reflected can be emitted fromthe optical element 12.

[0168] According to the structure, it is possible to obtain the samefunctions and effects as those in the case in which the lightinterference filter is used, and the optical element 12 for selecting anoptical path can be implemented at a low cost.

[0169] Referring to the cholesteric liquid crystal layer 30, moreover,in the case in which the spiral structure has a right twist, a lighthaving a right circular polarizing component is reflected and a lighthaving a left circular polarizing component along a spiral istransmitted. On the other hand, in the case in which the spiralstructure has a left twist, the light having the left circularpolarizing component is reflected and the light having the rightcircular polarizing component is transmitted. In the case in which alight having a total polarizing component is reflected, that is, is nottransmitted, accordingly, a total polarized light can be reflected bysuch a structure that a left twisted (or right twisted) cholestericlayer and the right twisted (or left twisted) cholesteric layer which isreverse thereto are sequentially superposed.

[0170] In addition to the cholesteric liquid crystal, a volume hologramis effective for the optical element having the function of the Braggreflection. The volume hologram has the Bragg reflecting function by agrating-shaped refractive index distribution formed in a film, andserves to reflect a specific wavelength. Moreover, when an incidenceangle is increased, the wavelength to be reflected is shifted toward theshort-wavelength side and the volume hologram functions as an opticalpath selecting film. The volume hologram can be formed by using, as aphotosensitive material, a photographic sensitive material for ahologram, a phase separation type photopolymer, an HPDLC (a holographicpolymer dispersing liquid crystal) or a photolithography material andcarrying out multiple beam interference exposure thereto.

[0171] Next, description will be given to a variant of the opticaldevice 100 according to the embodiment. FIG. 12 is a view showing thestructure of an optical device 200 according to the variant of theembodiment, in which an incident light is present in the optical device200. In other words, a light source is provided in the optical device200 in the structure. More specifically, there are a structure in whicha light source is sealed with a resin in the optical device 200 and astructure in which an optical element 10 itself for changing an opticalpath is a light emitting element. In this case, an incidence angle maybe a predetermined angle or an optional angle.

[0172] According to the variant, an incident light is diffused by theoptical element 10 for changing an optical path and is then irradiatedon the optical element 12 for selecting an optical path in variousincidence directions. Thereafter, the optical element 12 for selectingan optical path selectively transmits only an incident light having anangle component to be totally reflected by an interface 22 and reflectsincident lights having other angle components. Consequently, it ispossible to obtain the same functions and effects as described above.

[0173] In the structures of the optical device 100 according to thefirst embodiment and the optical device 200 according to the variant, atransparent medium 14 may be provided in the rear part of the opticalpath of the optical element 10 for changing an optical path. In thiscase, an interface generating a total reflection is set to be aninterface in the front part of the optical path of the optical element12 for selecting an optical path. Thus, it is preferable that theoptical device should have the optical element 10 for changing anoptical path and the optical element 12 for selecting an optical pathprovided in this order from the rear part of the optical path toward thefront part thereof, and an optional medium such as a transparent mediummay be provided between the laminated layers.

[0174] Next, description will be given to a second embodiment of theoptical device according to the invention.

[0175]FIG. 13 shows the structure of an optical device 300 according tothe embodiment. The optical device 300 according to the embodiment has amultilayer structure in which an optical element 10 for changing anoptical path, an intermediate transparent medium 32 having a refractiveindex of a glass substrate which is greater than 1, and an opticalelement 12 for selecting an optical path are provided in this order fromthe introduction side of an incident light. A transparent medium 16 ispresent in the front part of the optical path of the optical element 12for selecting an optical path in the optical device 300, and therelationship between a refractive index n3 of the optical element 12 anda refractive index n2 of the transparent medium 16 is set to satisfytotal reflecting conditions on the interface of the optical element 12and the transparent medium 16. Moreover, the incident light may bepresent on the outside or inside of the optical device 300, and may be acollimated light or a diffused light.

[0176] According to the optical device 300, the incident light isdiffused by the optical element 10 for changing an optical path and isthen irradiated on the optical element 12 for selecting an optical paththrough the intermediate transparent medium 32 in various incidencedirections. The refractive index of each medium is properly regulated ora reflection preventing treatment is carried out on each interface suchthat a total reflection is not substantially generated on an interfacewith the intermediate transparent medium 32. Thereafter, only a lighthaving an incidence angle component to be totally reflected in theoptical element 12 for selecting an optical path in the incident lightis transmitted through the optical element 12 and the transmitted lightis totally reflected by an interface 24 of the optical element 12 forselecting an optical path and the transparent medium 16, while anincident light component which does not satisfy the total reflectingconditions is reflected in the front part of the optical path of theoptical element 12 for selecting an optical path. Consequently, it ispossible to obtain the same functions and effects as described above.

[0177] Next, description will be given to a third embodiment of theoptical device according to the invention.

[0178]FIG. 14 shows the structure of an optical device 400 according tothe embodiment. The optical device 400 according to the embodiment has amultilayer structure in which an optical element 10 for changing anoptical path, an intermediate transparent medium 32 having a refractiveindex of a glass substrate which is greater than 1, an optical element12 for selecting an optical path which has a mean refractive index of n3and a transparent medium 34 having a refractive index of n4 are providedin this order from the introduction side of an incident light, and thetransparent medium 34 such as a transparent thin film is provided in thefront part of the optical path of the incident light in the opticaldevice 300 according to the second embodiment. The transparent medium 16is present in the front part of the optical path of the transparentmedium 34 in the optical device 400, and the relationship between therefractive index n4 of the transparent medium 34 and a refractive indexn2 of the transparent medium 16 is set to satisfy total reflectingconditions on the interface of the transparent medium 34 and thetransparent medium 16. Moreover, the incident light may be present onthe outside or inside of the optical device 400 and may be a collimatedlight or a diffused light.

[0179] According to the optical device 400 in accordance with theembodiment, the incident light is diffused by the optical element 10 forchanging an optical path and is then irradiated on the optical element12 for selecting an optical path through the intermediate transparentmedium 32 in various incidence directions. Thereafter, only a lighthaving an incidence angle component to be totally reflected by aninterface 25 of the transparent medium 34 and the transparent medium 16is transmitted by the optical element 12 for selecting an optical pathand the transmitted light is totally reflected by the interface 25 ofthe transparent medium 34 and the transparent medium 16, while anincident light component which does not satisfy the total reflectingconditions is reflected in the front part of the optical path of theoptical element 12 for selecting an optical path. Consequently, it ispossible to produce the same functions and effects as described above.

[0180] By regulating the refractive index of the transparent medium 34,it is possible to set an interface generating the total reflection intothe front part of the optical path of the transparent medium 34 or intothe interface of the optical element 12 for selecting an optical pathand the transparent medium 34.

[0181] The reflecting conditions of the transparent medium 34 will bedescribed below. FIG. 15 is a view showing a difference in an opticalpath for an incidence angle θ in the case in which the refractive indexn4 of the transparent medium 34 is smaller than the refractive index n3of the optical element 12 for selecting an optical path, and theincidence angle θ is gradually increased in order of (a) to (c). Thelight is reflected by the interface of the optical element 12 forselecting an optical path and the transparent medium 34 in the (a) inwhich the incidence angle θ is small, the light is transmitted throughthe interface and is totally reflected in the front part of the opticalpath of the transparent medium 34 in the (b), and the light is totallyreflected by the interface in the (c) in which the incidence angle θ isgreat. At this time, an incidence angle condition in each state is asfollows.

[0182] In the case of (a): θ≦sin⁻¹(1/n3)

[0183] In the case of (b): sin⁻¹(1/n3)<θ<sin⁻¹(n4/n3)

[0184] In the case of (c): sin⁻¹(n4/n3)≦θ

[0185] Moreover, FIG. 16 shows a difference in the optical path for theincidence angle θ in the case in which the refractive index n4 of thetransparent medium 34 is equal to or greater than the refractive indexn3 of the optical element 12 for selecting an optical path. In thiscase, the light is not totally reflected by the interface of the opticalelement 12 for selecting an optical path and the transparent medium 34.Similarly, the incidence angle condition in each state is as follows.

[0186] In the case of (a): θ≦sin⁻¹(1/n3)

[0187] In the case of (b) sin⁻¹(1/n3)<θ

[0188] By appropriately regulating the refractive index of thetransparent medium 34 depending on the situation of use of the opticaldevice, accordingly, it is possible to set the interface generating thetotal reflection into the front part of the optical path of thetransparent medium 34 or the interface of the optical element 12 forselecting an optical path and the transparent medium 34 and it ispossible to optionally set the interface generating the totalreflection.

[0189] The transparent medium 34 according to the embodiment may beprovided as a protective film for preventing the external damage ordeterioration of the optical element 12 for selecting an optical path ormay be a film having other functions, for example, a film having opticalor electrical functions. Moreover, the transparent medium 34 may beconstituted by a plurality of films.

[0190] The multipurpose transparent medium 34 may be provided in thefront part of the optical path of the transparent medium 16 in theoptical device 100 according to the first embodiment shown in FIG. 1.Also in this case, it is possible to obtain the same effects asdescribed above.

[0191] Next, description will be given to a fourth embodiment of theoptical device according to the invention.

[0192]FIG. 17 shows the structure of an optical device 500 according tothe embodiment. The optical device 500 according to the embodiment has amultilayer structure in which an optical element 10 for changing anoptical path, an optical connecting medium 36 such as an adhesive layer,an optical element 12 for selecting an optical path and a transparentmedium 14 such as a glass substrate are provided in this order from theintroduction side of an incident light, and the optical connectingmedium 36 is provided between the optical element 10 for changing anoptical path and the optical element 12 for selecting an optical path inthe optical device 100 according to the first embodiment. A transparentmedium 16 is present in the front part of the optical path of thetransparent medium 14 in the optical device 500, and the relationshipbetween a refractive index n4 of the transparent medium 14 and arefractive index n2 of the transparent medium 16 is set to satisfy totalreflecting conditions on an interface 22 of the transparent medium 14and the transparent medium 16. Moreover, an incident light may bepresent on the outside or inside of the optical device 500 and may be acollimated light or a diffused light.

[0193] According to the optical device 500 in accordance with theembodiment, the incident light is diffused by the optical element 10 forchanging an optical path and is then introduced through the opticalconnecting medium 36 into the optical element 12 for selecting anoptical path in various incidence directions. Thereafter, only a lighthaving an incidence angle component to be totally reflected by theinterface of the transparent medium 14 and the transparent medium 16 inthe front part of the optical path is transmitted by the optical element12 for selecting an optical path and the transmitted light is totallyreflected by the interface 22 of the transparent medium 14 and thetransparent medium 16, while an incident light component which does notsatisfy the total reflecting conditions is reflected in the front partof the optical path of the optical element 12 for selecting an opticalpath. Consequently, it is possible to obtain the same functions andeffects as described above.

[0194] The multipurpose transparent medium 34 according to the thirdembodiment may be provided in the front part of the optical path of thetransparent medium 14 according to the embodiment. Also in this case, itis possible to obtain the same effects as described above. By regulatingthe refractive indices of the transparent medium 34 and the transparentmedium 14, it is possible to set a total reflecting surface into thefront part of the optical path of the transparent medium 34 or theinterface of the transparent medium 14 and the transparent medium 34.

[0195] Next, description will be given to a fifth embodiment of theoptical device according to the invention.

[0196]FIG. 18 shows the structure of an optical device 600 according tothe embodiment. The optical device 600 according to the embodiment has amultilayer structure in which an optical element 10 for changing anoptical path, an optical connecting medium 36 such as an adhesive layer,an optical element 12 for selecting an optical path, a transparentmedium 14 such as a glass substrate and a medium 38 having a smallerrefractive index n5 than a refractive index n1 of the transparent medium14 are provided in this order from the introduction side of an incidentlight, and the medium 38 having a lower refractive index is provided inthe front part of an optical path for an incident light in the opticaldevice 500 according to the fourth embodiment. The relationship betweena refractive index n1 of the transparent medium 14 and a refractiveindex n5 of the medium 38 in the optical device 600 is set to satisfytotal reflecting conditions on an interface 39 of the transparent medium14 and the medium 38. Moreover, an incident light may be present on theoutside or inside of the optical device 500 and may be a collimatedlight or a diffused light.

[0197] According to the optical device 600 in accordance with theembodiment, the incident light is diffused by the optical element 10 forchanging an optical path and is then introduced through the opticalconnecting medium 36 into the optical element 12 for selecting anoptical path in various incidence directions. Thereafter, only a lighthaving an incidence angle component to be totally reflected by aninterface 39 of the transparent medium 14 and the medium 38 in the frontpart of the optical path is transmitted by the optical element 12 forselecting an optical path and the transmitted light is totally reflectedby the interface 39 of the transparent medium 14 and the medium 38. Onthe other hand, an incident light component which does not satisfy thetotal reflecting conditions is reflected in the front part of theoptical path of the optical element 12 for selecting an optical path.Consequently, it is possible to obtain the same functions and effects asdescribed above.

[0198] The medium 38 according to the embodiment may be provided as aprotective film for preventing the external damage or deterioration ofthe optical element 12 for selecting an optical path.

[0199] Next, description will be given to a sixth embodiment of theoptical device according to the invention.

[0200]FIG. 19 shows the structure of an optical device 700 according tothe embodiment. The optical device 700 according to the embodiment isprovided with a reflector 40 such as a diffusion reflector or a specularmirror which is opposed to the incident light introduction side of theoptical device 100 according to the first embodiment to reflect a light,and a light source 42 is provided between the reflector 40 and theoptical device 100. Accordingly, a light transmitted from the lightsource 42 is irradiated from the outside of the optical device 100. Thelight may be a collimated light or a diffused light.

[0201] According to the optical device 700 in accordance with theembodiment, the incident light transmitted from the light source 42 isirradiated on an optical element 10 for changing an optical path and isdiffused, and is then introduced into an optical element 12 forselecting an optical path in various incidence directions. Only a lighthaving an incidence angle component to be totally reflected by aninterface 22 of a transparent medium 14 and a transparent medium 16 inthe front part of an optical path is transmitted through the opticalelement 12 for selecting an optical path, and is totally reflected bythe interface 22 of the transparent medium 14 and the transparent medium16. On the other hand, an incident light component which does notsatisfy total reflecting conditions is reflected by the optical element12 for selecting an optical path. The reflected light is transmittedagain into the optical element 12 side for changing an optical path bymeans of the reflector 40 and is thus recycled. In the case in which thelight source 42 emits a diffused light, moreover, a light emitted to theopposite side to the optical element 12 side for changing an opticalpath is reflected by the reflector 40 and is thus recycled.Consequently, the light utilization efficiency of each of the lightsource 42 and the optical device 700 can be enhanced and the lightoutput intensity of the optical device 700 can be increased.

[0202] In addition to the foregoing, there are various combinations ofthe optical element for changing an optical path, the optical elementfor selecting an optical path and the transparent medium, andfurthermore, a total reflecting interface can also be proposedvariously. It is also possible to employ any combination which does notdepart from the scope of the invention.

[0203] Next, description will be given to a seventh embodiment accordingto the invention in which an optical device is constituted by using onlythe element for selecting an optical path in the optical element forchanging an optical path and the optical element for selecting anoptical path.

[0204]FIG. 20 shows the structure of an optical device 800 according tothe embodiment. The optical device 800 according to the embodiment has amultilayer structure in which a transparent base material 44 such as aglass substrate or a transparent resin, an optical element 12 forselecting an optical path and a transparent medium 14 having a totalreflecting surface are provided in this order from the introduction sideof an incident light. A transparent medium 16 is present in the frontpart of the optical path of the transparent medium 14 in the opticaldevice 800, and the relationship between a refractive index n4 of thetransparent medium 14 and a refractive index n2 of the transparentmedium 16 is set to satisfy total reflecting conditions on the interfaceof a transparent medium 34 and the transparent medium 16. Moreover, anincident light in this case has already been introduced into thetransparent base material 44 and is thus present. The presence can beimplemented by a structure in which a light is introduced from anotheroptical path into the transparent base material 44 or a structure inwhich a light emitting source is present in the transparent basematerial 44.

[0205] According to the optical device 800 in accordance with theembodiment, the incident light introduced into the transparent basematerial 44 is irradiated on the optical element 12 for selecting anoptical path in various directions. Then, only a light having anincidence angle component to be totally reflected by an interface 22 ofthe transparent medium 14 and the transparent medium 16 is transmittedby the optical element 12 for selecting an optical path and thetransmitted light is totally reflected by the interface 22 of thetransparent medium 14 and the transparent medium 16. On the other hand,an incident light component which does not satisfy the total reflectingconditions is reflected in the front part of the optical path of theoptical element 12 for selecting an optical path. Consequently, it ispossible to obtain the same functions and effects as described above.

[0206] It is also possible to employ such a structure that a mediumhaving a lower refractive index than a refractive index n1 of thetransparent medium 14 is provided in the front part of an optical pathfor the incident light of the transparent medium 14. Also in this case,the incident light introduced into the optical element 12 for selectingan outward route is reflected by a total reflection through theinterface 22 in the front part of the optical path of the transparentmedium 14.

[0207] Next, description will be given to a variant of the opticaldevice 800 according to the embodiment.

[0208]FIG. 21 shows the structure of an optical device 900 according tothe variant. The optical device 900 according to the variant has astructure in which an optical element 12 for selecting an optical pathis provided on a transparent medium 35 such as a glass substrate or atransparent resin. A transparent medium 16 is present in the front partof the optical path of the optical element 12 for selecting an opticalpath in the optical device 900, and the relationship between arefractive index n3 of the optical element 12 and a refractive index n2of the transparent medium 16 is set to satisfy total reflectingconditions on an interface 24 of the optical element 12 and thetransparent medium 16.

[0209] According to the optical device 900 in accordance with theembodiment, the incident light introduced into the transparent medium 35is irradiated on the optical element 12 for selecting an optical path invarious directions. Then, only a light having an incidence anglecomponent to be totally reflected by the interface 24 is transmitted bythe optical element 12 for selecting an optical path and the transmittedlight is totally reflected by the interface 24. On the other hand, anincident light component which does not satisfy the total reflectingconditions is reflected in the front part of the optical path of theoptical element 12 for selecting an optical path. Consequently, it ispossible to obtain the same functions and effects as described above.

[0210] Next, description will be given to an embodiment in which anoptical element for selecting an optical path which is used in theoptical device according to each of the first to seventh embodiments canbe implemented with a simple and inexpensive structure without using adielectric multilayer film and a cholesteric liquid crystal film.

[0211] First of all, description will be given to an eighth embodimentof the optical device according to the invention in which the opticaldevice is constituted by a transmission type diffraction grating.

[0212]FIG. 22 shows the structure of an optical device 1000 according tothe embodiment. The optical device 1000 according to the embodiment hasa multilayer structure in which a transparent base material 44 such as aglass substrate or a transparent resin, a transmission type diffractiongrating 46 and a medium 48 having a total reflecting surface areprovided in this order from the introduction side of an incident light.The incident light is a planar light ranging within a specific incidenceangle. In the case in which the transmission type diffraction grating 46is obtained by multiple hologram interference exposure, an optionalincidence angle may be set.

[0213] While the volume hologram shown in FIG. 2(a) can be preferablyused for the transmission type diffraction grating 46, it is alsopossible to use the relief type diffraction grating shown in FIG. 2(b),the refractive index distribution type diffraction grating shown in FIG.2(c) or an amplitude modulation type diffraction grating.

[0214] According to the optical device 1000 in accordance with theembodiment, when a planar incident light to be a collimated light isirradiated on the optical device 1000, it is transmitted through thetransparent base material 44 and an optical path is converted to havesuch an angle as to generate a total reflection in the medium 48 throughthe transmission type diffraction grating 46. In other words, thetransmission type diffraction grating 46 is designed such that theincident light has an angle at which the total reflection is generatedin the medium 48. By the transmission type diffraction grating 46, thus,it is possible to convert the incident light to have such an angle as togenerate the total reflection, thereby generating the total reflectionover the interface of the medium 48 in the front part of an optical pathfor the incident light.

[0215] Next, description will be given to a ninth embodiment of theoptical device according to the invention in which the optical device isconstituted by using a prism.

[0216]FIG. 23 shows the structure of an optical device 1100 according tothe embodiment. The optical device 1100 according to the embodimentcomprises a microprism array 50, and FIG. 23(a) is a plan view showingthe microprism array 50 seen from the incidence surface side of a lightand FIG. 23(b) is a sectional view showing a P-P section in (a).

[0217] The microprism array 50 is plate-shaped and has such aconfiguration that an upper surface is set to be a flat total reflectingsurface 52 and a lower surface is provided with a plurality ofconcavo-convex prisms 54 having a cone-shaped section in parallel.

[0218] Examples of the material of the microprism array 50 include aglass and a resin, and particularly, the resin is preferable in respectof mass production. For the resin, acryl based resins, epoxy basedresins, polyester based resins, polycarbonate based resins, styrenebased resins and vinyl chloride based resins are optically preferable,and furthermore, examples of the resin material include a photo-curingtype, a photo-dissolving type, a thermosetting type and a thermoplastictype which can be selected appropriately.

[0219] As a method of manufacturing the microprism array 50, castingusing a mold, hot press molding, injection molding, printing orphotolithography is preferable in respect of a productivity

[0220] More specifically, formation can be carried out by pressing athermoplastic resin in a microprism-shaped mold. Moreover, the formationcan be carried out by filling the mold with a photo-curing resin or athermosetting resin and then curing the resin through a light or heatand removing the cured resin from the mold.

[0221] For the photolithography, the formation is carried out byexposing an ultraviolet radiation (or a visible light) to aphoto-dissolving resin or a photo-curing resin through a shielding maskpatterned properly and performing a dissolving development in theexposed portion or the dissolving development in an unexposed portion.It is possible to obtain a microprism having a desirable shape by aresin material and an exposure amount distribution. Depending on theresin material, moreover, it is possible to carry out a high temperaturebaking treatment after the development, thereby obtaining the microprismarray 50 having a desirable shape by a surface tension duringthermosoftening.

[0222] Furthermore, the incident light is a planar light ranging withina specific incidence angle and is incident on the optical device 1100 atan incidence angle θ_(i) as shown in FIG. 23(b).

[0223] According to the optical device 1100 in accordance with theembodiment, in the case in which a medium present around the microprismarray 50 is air (a refractive index n2=1) and the microprism array 50 isformed of a transparent resin (a refractive index n7=1.5), a totalreflecting critical angle θ_(C) on a total reflecting surface 52 iscalculated in the same manner as in the equation (1) to be 42 [deg].

[0224] As an example for setting an incidence angle θ for the totalreflecting surface 52 to be θ≧θ_(C), therefore, a vertical angle α ofthe prism is set to be approximately 90 [deg] and a lateral openingangle is set to be approximately 45 [deg]. In this case, when theincident light is incident from the outside of the prism, the incidenceangle θ_(i) of the incident light is set to be approximately 45 [deg].Under this condition, an optical shading is not substantially generatedbut the incident light can be totally reflected efficiently by the totalreflecting surface 52. The vertical angle α of the prism is notrestricted thereto.

[0225] By using the microprism array 50 which can be mass producedeasily and inexpensively, consequently, it is possible to introduce anincident light to be irradiated like a plane and to totally reflect thesubstantially whole incident light thus introduced.

[0226] Next, description will be given to a tenth embodiment of theoptical device according to the invention in which the optical device isconstituted by using the microprism array according to the ninthembodiment.

[0227]FIG. 24 shows the sectional structure of an optical element 1200according to the embodiment and FIG. 25 shows the conceptional wholestructure of the optical element 1200. The optical element 1200according to the embodiment has a lamination structure in which amicroprism array 50 and a transparent medium 56 such a glass or a resinare provided from the introduction side of an incident light.

[0228] A transparent medium 16 is present in the front part of theoptical path of the transparent medium 56 in the optical element 1200,and the relationship between a refractive index n8 of the transparentmedium 56 and a refractive index n2 of the transparent medium 16 is setto satisfy total reflecting conditions on the interface of thetransparent medium 56 and the transparent medium 16. Moreover, anincident light is a planar light ranging within a specific incidenceangle.

[0229] According to the optical element 1200 in accordance with theembodiment, the planar incident light is irradiated on the microprismarray 50 and an incident light having a predetermined incidence anglecomponent set by a vertical angle α of a prism by means of themicroprism array 50 is introduced into the transparent medium 56. Then,the incident light thus introduced is totally reflected efficiently by atotal reflecting surface 58 of the transparent medium 56.

[0230] By using the microprism array 50 which can be mass producedeasily and inexpensively to introduce an incident light to be irradiatedlike a plane, thus, it is possible to totally reflect the substantiallywhole introduced incident light by the interface 58 of the transparentmedium 56.

[0231] Next, description will be given to an eleventh embodiment of theoptical device according to the invention in which an optical elementfor changing an optical path at an angle corresponding to the lightincidence angle of a microprism array 50 is provided in the front partof the optical path of the optical element 1200 according to the tenthembodiment, thereby constituting the optical device.

[0232]FIG. 26 shows the sectional structure of an optical device 1300according to the embodiment. The optical device 1300 according to theembodiment comprises an optical element having a transparent basematerial 60 such as a glass substrate or a transparent resin and atransmission type diffraction grating 62 provided in this order and theoptical element 1200 according to the tenth embodiment from theintroduction side of an incident light. The incident light is a planarlight ranging within a specific incidence angle.

[0233] While a volume hologram can be preferably used for thetransmission type diffraction grating 62 in the same manner as thetransmission type diffraction grating 46 according to the seventhembodiment, it is also possible to use a relief type diffractiongrating, a refractive index distribution type diffraction grating or anamplitude modulation type diffraction grating.

[0234] According to the optical device 1300 in accordance with theembodiment, when a planar incident light to be a collimated light isirradiated on the optical device 1300, it is transmitted through thetransparent base material 60 and an optical path is converted into alight having a predetermined incidence angle component set by a verticalangle α of a microprism array 50 by the transmission type diffractiongrating 62. More specifically, the optical path is converted to havesuch an angle as to generate a total reflection by an interface 58 of atransparent medium 56. In other words, the transmission type diffractiongrating 62 is designed such that an incident light has an angle at whicha total reflection is generated by the interface 58 of the transparentmedium 56. By converting the incident light to have such a predeterminedincidence angle as to be introduced into the microprism array 50 by thetransmission type diffraction grating 62, thus, it is possible tototally reflect the introduced incident light by the interface 58 of thetransparent medium 56.

[0235] The optical device according to the invention described above canbe applied to a reflector such as a visible transparent film forreflecting an infrared light, a high efficient reflecting film, a highefficient reflecting film having a wavelength selectivity or a reflectoror film for a light source having a high efficiency, an indicator suchas a decorative illumination advertisement display utilizing a planartotal reflected light, an optical modulating element and a planedisplay, for example.

[0236] Description will be given to a specific example of the structureof the optical device according to the invention and a result obtainedby calculating, through a simulation, the spectral transmittance of theoptical device according to the example of the structure.

[0237]FIG. 27 shows an example of the structure of the optical deviceaccording to the invention. In the optical device in this case, a lightdiffusing film (a refractive index n=1.5) to be an optical element forchanging an optical path, a dielectric multilayer film to be an opticalelement for selecting an optical path and a glass substrate (arefractive index n=1.5) are sequentially provided from the introductionside of an incident light. Air (a refractive index n=1.0) is present inthe front part of the optical path of the glass substrate.

[0238] The dielectric multilayer film has a 29-layer structure ofTiO₂/SiO₂/ . . . /SiO₂/TiO₂ and the optical thickness of each layer isset to be {fraction (1/4)} (a wavelength λ=440 [nm]). Moreover, a UVlight source having a wavelength λ=350 to 400 [nm] shown in FIG. 28 wasused for the incident light. In this case, a total reflecting criticalangle θ_(C) is set to be approximately 40 [deg].

[0239] The spectral transmittance of an optical device (a dielectricmultilayer film) was calculated under the condition described above sothat results shown in FIGS. 29 and 30 were obtained. FIG. 29 is a graphshowing a change in a spectral transmittance T for the wavelength λevery incidence angle θ and FIG. 30 is a graph showing the spectraltransmittance T for the incidence angle θ every wavelength λ.

[0240] As shown in FIG. 29(a), in the case in which the incidence angleθ is 0 [deg], the spectral transmittance T in the wavelength area of theUV light source is approximately 0 [%] and a light is not transmittedthrough the optical device. Also in the case in which the incidenceangle θ is 40 [deg] immediately before the total reflecting criticalangle θ_(C) as shown in FIG. 29(b), moreover, the light is nottransmitted through the optical device. In the case in which theincidence angle θ is 70 [deg] as shown in FIG. 29(c), a spectraltransmittance of approximately 100 [%] is obtained for a P wave and aspectral transmittance of approximately 0 [%] is obtained for an S wave,and the average of the P wave and the S wave is approximately 50 [%].

[0241] Moreover, in the case in which a wavelength on theshort-wavelength side in the wavelength area of the UV light source isset to be λ=350 [nm] as shown in FIG. 30(a), the spectral transmittancefor the P wave is enhanced with an incidence angle θ of approximately 50[deg] or more. In the case in which a central wavelength is set to beλ=375 [nm] shown in FIG. 30(b), the spectral transmittance is enhancedwith an incidence angle θ of approximately 46 [deg] or more.Furthermore, in the case in which a wavelength on the long-wavelengthside is set to be λ=400 [nm] shown in FIG. 30(c), the spectraltransmittance is enhanced with an incidence angle θ of approximately 42[deg] or more.

[0242] By carrying out a total reflection through the optical deviceusing the P wave or changing various conditions of the optical device toproperly design the spectral characteristic of the S wave into a closecharacteristic to the P wave, it is possible to selectively reflect anincident light in the wavelength area of the UV light source at theincidence angle θ which is equal to or smaller than the total reflectingcritical angle θ_(C) and to transmit the same incident light at agreater angle than the total reflecting critical angle θ_(C).Consequently, the dielectric multilayer film of the optical device canbe caused to function as an optical element for selecting an opticalpath sufficiently in practical use.

[0243] While the invention has been described in detail with referenceto the specific embodiments, it is apparent to the skilled in the artthat various changes and modifications can be made without departingfrom the spirit and scope of the invention.

[0244] The invention is based on Japanese Patent Application(JP-A-2000-374527) filed in Dec. 8, 2000 and contents thereof areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

[0245] According to the invention, the optical device is plane-shaped.When an incident light is introduced like a plane into the opticaldevice, at least a part of the incident light thus introduced is totallyreflected by the interface of layers constituting the optical device andis then returned to the incident light introduction side, and theincident light introduced into the optical device is not substantiallyemitted from the opposite side to the incident light introduction side.For this reason, the introducing position of the incident light is notrestricted, for example, the incident light does not need to beintroduced at a greater angle than the total reflecting critical anglefrom the end face of the optical device, and furthermore, the type ofthe light source is not limited, for example, the incident light doesnot need to take the shape of a beam or a line. Consequently, the planarincident light can be introduced like a plane directly and efficientlywithout using a light guiding plate or an optical waveguide, and aplanar total reflected light can be obtained efficiently on a desirableinterface. Moreover, since at least a part of the incident lightintroduced into the optical device is reflected by a total reflection,the optical device can be caused to function as an efficient reflectorhaving neither an incidence angle dependency nor an absorption.

[0246] In the optical device according to the invention, moreover, theoptical element for changing an optical path is provided in the opticaldevice and the incident light is introduced like a plane into theoptical element for changing an optical path. The optical path for theincident light thus introduced is changed into a specific direction oran optional direction by the optical element for changing an opticalpath, and the substantially whole incident light is reflected throughthe total reflection by the interface of the layers constituting theoptical device. According to the structure, the introducing position ofthe incident light is not restricted and the type of the light source isnot limited, and the planar incident light can be introduced like aplane directly and efficiently without using a light guiding plate or anoptical waveguide. Moreover, the optical device can be caused tofunction as an efficient reflector having neither an incidence angledependency nor an absorption.

[0247] In the optical device according to the invention, furthermore,the optical element for selecting an optical path is provided in theoptical device and the incident light is introduced like a plane intothe optical element for selecting an optical path. The optical path forthe incident light thus introduced is changed into a specific directionor an optional direction by the optical element for selecting an opticalpath, and the substantially whole incident light is reflected throughthe total reflection by the interface of the layers constituting theoptical device. According to the structure, the introducing position ofthe incident light is not restricted and the type of the light source isnot limited, and the planar incident light can be introduced like aplane directly and efficiently without using a light guiding plate or anoptical waveguide. Moreover, the optical device can be caused tofunction as an efficient reflector having neither an incidence angledependency nor an absorption.

[0248] In the optical device according to the invention, moreover, theoptical element for changing an optical path and the optical element forselecting an optical path are provided in this order from the incidentlight introduction side in the direction of the thickness of the opticaldevice, and the incident light is introduced like a plane into theoptical element for changing an optical path. The optical path for theincident light thus introduced is changed into a specific direction oran optional direction by the optical element for changing an opticalpath, and furthermore, only the incident light in the specific directionis transmitted through the optical element for selecting an optical pathso that the substantially whole light introduced into the optical deviceis reflected through the total reflection by the interface of the layersconstituting the optical device. Also in such a structure, theintroducing position of the incident light is not restricted and thetype of the light source is not limited, and the planar incident lightcan be introduced like a plane directly and efficiently without using alight guiding plate or an optical waveguide. Moreover, the opticaldevice can be caused to function as an efficient reflector havingneither an incidence angle dependency nor an absorption.

[0249] In the optical device according to the invention, furthermore,the optical element for introducing an incident light to be totallyreflected by the interface of the layers constituting the optical deviceis provided in the optical device and the incident light is introducedlike a plane into the optical element for introducing the incidentlight. The incident light thus introduced is reflected through the totalreflection by the interface of the layers constituting the opticaldevice. With a simple structure, consequently, the introducing positionof the incident light is not restricted and the type of the light sourceis not limited, and the planar incident light can be introduced like aplane directly and efficiently without using a light guiding plate or anoptical waveguide. Moreover, the optical device can be caused tofunction as an efficient reflector having neither an incidence angledependency nor an absorption.

What is claimed is:
 1. A planar optical device characterized by such a feature that when an incident light is introduced like a plane into the optical device, at least a part of the incident light thus introduced is totally reflected by an interface of layers constituting the optical device, while the incident light is not substantially emitted from an opposite side to an incident light introduction side.
 2. A planar optical device characterized in that an optical element for changing an optical path is provided in the optical device, and at least a part of a planar incident light introduced in the optical device is introduced into the optical element for changing an optical path and the substantially whole incident light thus introduced is totally reflected by an interface of layers constituting the optical device.
 3. A planar optical device characterized in that an optical element for selecting an optical path is provided in the optical device, and at least a part of a planar incident light introduced in the optical device is introduced into the optical element for selecting an optical path and the substantially whole incident light thus introduced is totally reflected through a total reflection by an interface of layers constituting the optical device.
 4. A planar optical device characterized in that an optical element for changing an optical path and an optical element for selecting an optical path are provided in this order from an incident light introduction side in a direction of a thickness of the optical device, and when an incident light is introduced like a plane into the optical element for changing an optical path, at least a part of the incident light thus introduced is introduced into the optical element for selecting an optical path and the substantially whole incident light thus introduced is reflected through a total reflection by an interface of layers constituting the optical device.
 5. The optical device according to any of claims 1 to 4, wherein the substantially whole incident light which is reflected totally is returned to the incident light introduction side of the optical device.
 6. The optical device according to any of claims 1 to 4, wherein the layer constituting the optical device is not substantially absorbed into a wavelength area of the incident light.
 7. The optical device according to claim 4, wherein the optical element for changing an optical path and the optical element for selecting an optical path are provided in optical contact with each other.
 8. The optical device according to claim 4, wherein the optical element for changing an optical path and the optical element for selecting an optical path are provided in optical contact with each other through a medium having a greater refractive index than
 1. 9. The optical device according to claim 2 or 4, further comprising a transparent medium constituting a part of the optical device, the optical element for changing an optical path being provided in a front part of an optical path of the transparent medium.
 10. The optical device according to any of claims 3 to 4, further comprising a transparent medium constituting a part of the optical device, the optical element for selecting an optical path being provided in a front part of an optical path of the transparent medium.
 11. The optical device according to claim 4, further comprising a transparent medium constituting a part of the optical device, the optical element for changing an optical path and the optical element for selecting an optical path being provided in this order in a front part of an optical path of the transparent medium.
 12. The optical device according to any of claims 1 to 4, wherein a medium constituting apart of the optical device is provided in a frontmost part of the optical path of the optical device, and a front or rear interface of an optical path for an incident light of the medium is set to be an interface generating the total reflection.
 13. The optical device according to claim 12, wherein, for the interface generating the total reflection, a rear part of the optical path for the incident light is selected with na>nb if sin⁻¹(nb/na)≦θ is set, and a front part of the optical path for the incident light is selected with na>nb if sin⁻¹(1/na)<θ<sin⁻¹(nb/na) is set, and the front part of the optical path for the incident light is selected with na≦nb if sin⁻¹(1/na)≦θ set, in which nb represents a mean refractive index of the medium, na represents a mean refractive index of a layer provided in the rear part of the optical path of the medium, and θ represents an angle of a light advancing in the layer of the rear part of the optical path.
 14. The optical device according to any of claims 1 to 4, wherein the interface generating the total reflection is set to be an interface of a medium having a first refractive index constituting a part of the optical device and a medium provided in a front part of the optical path for the incident light in contact with the medium and having a second refractive index which is smaller than the first refractive index.
 15. The optical device according to any of claims 1 to 4, wherein the interface generating the total reflection is a frontmost surface of the optical path for the incident light of the optical device.
 16. The optical device according to claim 15, wherein the interface generating the total reflection has a forward side of the optical path for the incident light to be an air contact interface.
 17. The optical device according to claim 2 or 4, wherein the optical element for changing an optical path includes and forward outputs a light having an angle θt to satisfy at least a condition of sin θt>nw/nt, in which nt represents a mean refractive index of the optical element for changing an optical path, nw represents a refractive index of a medium on a forward side of a total reflecting interface in a front part of the optical path, and θt represents an angle of a light advancing in a medium of the optical element for changing an optical path.
 18. The optical device according to claim 2 or 4, wherein the optical element for changing an optical path serves to change the optical path by a refraction.
 19. The optical device according to claim 18, wherein the optical element for changing an optical path is any of a lens array, a prism array and a heterorefractive index distribution member having various refractive indices distributed.
 20. The optical device according to claim 2 or 4, wherein the optical element for changing an optical path serves to change the optical path by a diffraction.
 21. The optical device according to claim 20, wherein the optical element for changing an optical path is any of a volume hologram, a phase modulation type diffraction grating and an amplitude modulation type diffraction grating.
 22. The optical device according to any of claims 2 to 4, wherein the optical element for changing an optical path serves to change an optical path by a light diffusion.
 23. The optical device according to claim 22, wherein the optical element for changing an optical path is a porous member, a heterorefractive index distribution member, a dispersion member, a diffusion member having a concavo-convex surface or a scattering member.
 24. The optical device according to any of claims 2 to 4, wherein the optical element for changing an optical path serves to change an optical path by a light reflection.
 25. The optical device according to claim 3 or 4, wherein the optical element for selecting an optical path has such a feature that a substantially whole transmitted light which is emitted from the optical element has a greater angle component than a total reflecting critical angle on an interface of layers in a front part of an optical path for the incident light from the optical element for selecting an optical path or an interface in a front part of the optical path for the incident light of the optical element for selecting an optical path and incident lights having other angle components are selectively reflected and are not transmitted.
 26. The optical device according to claim 3 or 4, wherein the optical element for selecting an optical path transmits a substantially whole light having an angle θs to satisfy a condition of sin θs>nw/ns, in which ns represents a mean refractive index of the optical element for selecting an optical path, nw represents a refractive index of a medium on a forward side of a total reflecting interface in a front part of the optical path, and θs represents an angle of a light advancing in the medium of the optical element for selecting an optical path.
 27. The optical device according to claim 3 or 4, wherein the optical element for selecting an optical path has a function of selectively carrying out a reflection for a wavelength area of an incident light, and a wavelength of the incident light to be reflected selectively is shifted toward a short-wavelength side when an incidence angle of the incident light on the optical element for selecting an optical path is reduced with respect to a surface of the optical element.
 28. The optical device according to claim 3 or 4, wherein when an incidence angle of the incident light on a total reflecting interface in a front part of an optical path for the incident light in the optical element for selecting an optical path is equal to or smaller than a total reflecting critical angle, the optical element for selecting an optical path selectively reflects the substantially whole incident light.
 29. The optical device according to claim 3 or 4, wherein the optical element for selecting an optical path is a light interference filter including a dielectric multilayer film.
 30. The optical device according to claim 3 or 4, wherein the optical element for selecting an optical path is a Bragg reflecting filter including a cholesteric liquid crystal and a volume hologram.
 31. A planar optical device characterized in that an optical element for introducing an incident light is provided in the optical device, and when the incident light is introduced like a plane into the optical element for introducing the incident light, the substantially whole incident light thus introduced is reflected through a total reflection by an interface of layers constituting the optical device.
 32. The optical device according to claim 31, wherein the optical element for introducing an incident light is a prism array arranged like a plane.
 33. The optical device according to any of claims 1-4 or 31, wherein the incident light is a collimated light ranging within a specific incidence angle.
 34. The optical device according to claim 32, wherein the incident light is a collimated light having a plurality of incidence angles.
 35. The optical device according to any of claims 1, 3 to 4 or 31, wherein the incident light is a diffused light having an optional incidence angle.
 36. The optical device according to any of claims 1 to 4 or 31, wherein a light source is provided in the optical device and the incident light is emitted from the light source.
 37. The optical device according to any of claims 1 to 4 or 31, wherein the incident light is incident from an outside of the optical device.
 38. The optical device according to any of claims 1 to 4 or 31, wherein a reflector for transmitting, toward the optical device side again, a light which is once incident on the optical device and is reflected by the optical device is provided opposite to an incident light introduction side of the optical device.
 39. The optical device according to any of claims 1 to 4 or 31, wherein the incident light is any of a UV light, a visible light and an infrared light.
 40. The optical device according to any of claims 1 to 4 or 31, wherein the incident light is emitted from any of a discharge lamp, a laser beam source, an LED, an inorganic or organic EL, an incandescent lamp, a cathode-ray lamp and an FED. 